No. 61: Jan-Feb 1989
An advanced lidar device, located at Urbana, Illinois, has been sending pulses of light up into the atmosphere and measuring the reflections from atmospheric atoms and molecules. To the researchers' surprise, this instrument detected sudden appearances of clouds of sodium atoms at about 85 kilometers altitude. The clouds quickly dissipate, but where do they come from? The best guess is that their source is meteors vaporizing in the upper atmosphere.
(Raloff, Janet: "Sudden Sodium Surges Seen over Illinois," Science News, 134: 238, 1988.)
Comment. Could these sodium clouds have any connection with the controversial icy comets?